A. There are two forms of dietary iron, “heme” iron and
“non-heme” iron. Heme iron is iron bound to hemoglobin (the oxygen
transporting protein in blood); non-heme iron is not bound to hemoglobin. Heme
iron is the most efficiently absorbed form of iron. The absorption rate of
non-heme iron supplements, such as ferrous sulfate and ferrous fumarate, is 2.9%
on an empty stomach and 0.9% with food. This is much less than the absorption
rate of heme iron, as found in liver, which is as high as 35%. In addition, heme
iron is without the side effects associated with non-heme sources of iron, such
as nausea, flatulence, and diarrhea.

Despite the superiority of heme iron, non-heme iron salts are the most
popular iron supplements. One reason is that even though heme-iron is better
absorbed, it is easy to take higher quantities of non-heme iron salts so that
the net amount of iron absorbed is about equal. In other words, if you take 3 mg
of heme iron and 50 mg of non-heme iron, the net absorption for each will be
about the same. The best form of non-heme iron is ferrous succinate. Consult a
healthcare professional before taking iron supplements.

Michael Murray, ND, is one of the world’s leading authorities on natural medicine and a contributor to the
Healthnotes, Inc. team of experts. Dr. Murray is the author of A
Textbook of Natural Medicine,Encyclopedia of Natural Medicine,
and The Healing Power of Herbs. He also authors Dr. Murray’s
Electronic Encyclopedia of Natural Medicine, an exclusive
Healthnotes product.